This project involves clinical and immunologic studies of humans infected with the intestinal nematode, Strongyloides stercoralis, and parallel studies in an experimental host, the patas monkey. Research on this parasite is justified because human infections occur in substantial numbers even in the U.S., it often goes undiagnosed and can produce fatal outcome in immunosuppressed people, and it is a parasite with unusual biologic properties. A good portion of the somatic and E/S antigens obtained from infected patas monkeys in the pat year is being stockpiled for a new batch of skin test antigen. Antigenic analysis of infective larvae (L3) has focused heavily upon identification and characterization of a protease present in both somatic and E/S antigens. It is a metallo-protease with functional activity demonstrable at about 30, 60, and 90 kD, suggesting a trimeric form. The protease is also allergenic -- i.e., it causes histamine release from IgE sensitized basophils in-vitro. Monoclonal antibodies raised to somatic larval antigen have been relatively weak in identifying antigens, and IgE Western blots are faint so that these reagents and approaches have not been as useful as expected. The possibility that HTLV-1 infection may selectively impair immune responses important for control of strongyloidiasis in some patients is being investigated.